Firefox OS 1.3 现在处于预发布的阶段。它的 Gecko 组件是基于Firefox 28(见Firefox开发人员28日发布说明https://developer.mozilla.org/en-US/Firefox/Releases/28。)
Firefox OS 1.3 主要包括 CSS，JavaScript ，HTML，DOM/API ，音频和视频方面的 bug 修复，一些新特性和其他一些功能改进。主要更新内容如下：
CSS
General Gecko:
Support for multi-line flexbox has been added (bug 939901).
Longhand East Asian counter styles have been implemented (bug 934072).
Support for the background-blend-mode property has been added (bug 841601).
The none value has been added to font-variant-ligatures (bug 913264).
Support for the :hover user action pseudo-class on pseudo-elements has been implemented (bug 922669).
The -moz-grab and -moz-grabbing keywords on the CSS cursor property have been unprefixed to grab and grabbing (bug 880672).
Support for the -moz-hsla() and -moz-rgba() functional notations has been dropped. Only the unprefixed versions, hsla() and rgba() are supported from now on (bug 893319).
The "true" value for text-align has been added (bug 929991).
Experimental support of position:sticky is now active by default on non-release builds (bug 902992). For releases builds, the layout.css.sticky.enabled preference still needs to be set to true.
The all shorthand property has been added (bug 920633).
The unset global value has been added; it allows to reset any CSS property (bug 921731).
Curly brackets are no longer allowed in HTML style attributes: doing
